1. Field of the Invention
This invention is an improved process for the production of metal alkoxides, more particularly antimony glyoxides. These compounds have utility as catalysts. They are especially useful as catalysts for the polymerization of glycols and diacids or their derivatives to make polyesters. Antimony glyoxides can be made by the reaction of antimony halides or oxides with ethylene glycol, propylene glycol, or their alkali metal glycolates (glyoxides). The straight chemical approach leads to the formation of unwanted by-products and impure antimony glyoxide which must be purified. More elegant is an electrochemical synthesis employing antimony anodes in a glycol medium whereby the major by-product is hydrogen, which does not contaminate the product.
2. Description of the Prior Art
The electrochemical preparation of metal organic compounds has been disclosed in U.S. Pat. No. 3,964,983 granted June 22, 1976 to Eisenbach et al. This disclosure includes a wide variety of active hydrogen compounds with a pk (negative logarithm of the acidity) from 5 to 20 and metals with a standard potential more positive than -1.66 volts. Furthermore it discloses and claims that water is sometimes a beneficial component of the electrolyte. "Diaphragms" are sometimes employed by Eisenbach et al, but are never described.
Production of monohydric alkoxides is disclosed in a method published in U.S. Pat. No. 3,730,857 granted May 1, 1973 to Tripp. This disclosure encompasses metals of Group IV or Va of the periodic table of the elements with atomic numbers from 14 to 82. No "diaphragms" or separators are mentioned in this patent. Ethylene glycol is characterized as "inert" by Tripp, even when present as 25 percent of the electrolyte. Only monohydric compounds are disclosed or claimed as being operative, and the examples disclose only preparation of ethoxides.
The use of ion-exchange membranes as separators in the electrochemical preparation of organometal compounds is disclosed in U.S. Pat. No. 3,197,392 granted July 27, 1965 to Silversmith and Sloan. This disclosure is limited to hydrocarbons as reagents for making organometals of the tetraethyl lead type. The patent teaches that anion-exchange membranes and cation-exchange membranes are interchangeable equivalents. No distinction is made by Silversmith et al between ion-permeable separators which are uncharged such as porous porcelain, asbestos, parchment, polyethylene, glass fiber paper, and the like, which allow ions to pass indiscriminately, and ion-exchange membranes which prevent the passage of some ions on a selective basis.
3. Objects of the Invention
The principal object of this invention is to provide an improved process to produce metal alkoxides, electrochemically, at an anode while limiting reduction to metal at the cathode, which may contaminate the desired metal alkoxide. Another object of this invention is to provide a process with improved electrolytic efficiency for the synthesis of metal alkoxides. An additional object of this invention is to improve the yield of the desired alkoxide by substantially reducing formation of colloidal metal. A further object of the invention is to obviate the formation of potentially explosive colloidal metal, particularly antimony. Still another object of this invention is to provide a process for electrochemical synthesis which operates for long periods of time without the formation of impeding precipitates. Other objects will be apparent to one skilled in the art from the description and examples which follow.